Display device and manufacturing method thereof

ABSTRACT

A plurality of display panels having a curved surface are placed in a limited space. Two, or three or more display panels are combined to form one display region having a T-shaped outer edge as one screen, and a driver can curve part of the display panel as appropriate so that the driver can see the screen easily. A first display panel or a second display panel has flexibility and includes a position adjustment function of curving an end portion. That is, by curving part of the display panel, the user can see the display panel easily. The in-car design can also be varied.

TECHNICAL FIELD

The technical field of one embodiment of the invention disclosed in thisspecification and the like relates to an object, a method, or amanufacturing method. Alternatively, one embodiment of the presentinvention relates to a process, a machine, manufacture, or a compositionof matter. Thus, more specifically, examples of the technical field ofone embodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a light-emittingdevice, a lighting device, a power storage device, a memory device, adriving method thereof, and a manufacturing method thereof. Note thatone embodiment of the present invention is not limited to the abovetechnical field.

Note that in this specification, a semiconductor device refers to alldevices which can function by utilizing semiconductor characteristics,and electro-optical devices, semiconductor circuits, and electronicdevices are all semiconductor devices.

BACKGROUND ART

Development is advanced so that an instrument display in a car or thelike is partly replaced with a liquid crystal display device. Display ina car has been utilized and approaches to supporting a driver of avehicle such as a car have been taken to use more information (e.g.,information on the situation around the car, traffic information, andgeographic information).

A number of cameras and sensors will be installed inside and outside acar in the future.

A display panel having a curved surface is disclosed in PatentDocument 1. A structure in which a plurality of display panels overlapwith one another is disclosed in Patent Document 2. A display devicehaving a non-rectangular display region is disclosed in Patent Document3.

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2003-229548-   [Patent Document 2] Japanese Published Patent Application No.    2014-197179-   [Patent Document 3] Japanese Published Patent Application No.    2015-180924

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In order to perform display warning a driver of a risk depending on thesituation obtained from a variety of cameras and sensors, the areas ofdisplay regions corresponding to the numbers of cameras and sensors areneeded. However, the inside of a car is a limited space surrounded bywindows or the like, and the place where a display portion can beinstalled inside a car has a variety of uneven surfaces including acurved surface.

When a display panel having a plane with a large display area and alarge thickness is installed on a dashboard, a driver's field of visionis obstructed.

Means for Solving the Problems

A plurality of display panels having a curved surface are placed in alimited space. The plurality of display panels include a region where atleast two display panels overlap with each other. At least one of theplurality of display panels has a curved surface, and the other displaypanels may have a flat surface.

Two, or three or more display panels are combined to form one displayregion having a T-shaped outer edge. Thus, two systems or three or moresystems of video signals, which correspond to the number of combineddisplay panels are used for one display region having a T-shape.

When a driver considers that display of the entire screen isunnecessary, a period in which power supplied to one of the plurality ofdisplay panels that form one display region is set to zero is providedbecause each display region can be turned on or off as necessary, sothat power consumption can also be reduced.

According to one embodiment of the present invention of a display devicethat includes a first display panel, a second display panel, and a thirddisplay panel, the first display panel includes a first region and asecond region; the second display panel includes a third region and afourth region; the third display panel includes a fifth region and asixth region; the first region, the third region, and the fifth regioneach have a function of transmitting visible light; the second region,the fourth region, and the sixth region each have a function ofperforming display; a first portion in which the first region of thefirst display panel and the fourth region of the second display paneloverlap with each other is included; a second portion in which the fifthregion of the third display panel and the second region of the firstdisplay panel overlap with each other is included; a third portion inwhich the fifth region of the third display panel and the fourth regionof the second display panel overlap with each other is included; and onedisplay region including the second region, the fourth region, and thesixth region has a substantial T-shape.

It is preferable to fix a plurality of display panels to a curvedsurface of a car dashboard, or the like, and overlap end portions of theplurality of display panels to obtain one display region. Each displaypanel is desired to be thin so that a transmissive region in theperiphery of a display region of one display panel and a display regionof an adjacent display panel overlap with each other. Therefore, for thedisplay panel, an active matrix display panel using an organiclight-emitting element formed over a plastic film is suitable.

In the above structure, in order to overlap the end portions of theplurality of display panels, one feature is that a fourth portion inwhich the fifth region of the third display panel, the third region ofthe second display panel, and the first region of the first displaypanel overlap with one another is included and the fourth portion isplaced between the second portion and the third portion.

In the case of overlapping the end portions of the plurality of thedisplay panels and displaying one video, a display seam might be causedwhen display of the entire screen is performed. It is preferable tocombine two, or three or more display panels and adjust discontinuity ofvideo at the seam between the display regions of the adjacent displaypanels so that a user does not recognize it easily. In particular, inthe case where the display panels are high-resolution panels, forexample, a plurality of display panels are combined from a 2K displaypanel in which the number of pixels is 1920×1080, a 4K display panel inwhich the number of pixels is 3840×2160 or 4096×2160, and a 8K displaypanel in which the number of pixels is 7680×4320 or more, it ispreferable to use artificial intelligence (AI) to adjust discontinuityof the video so that a user does not recognize it easily.

Against a problem of discontinuity of the video at the seam, a displaysystem including a display device in which a plurality of display panelsaccording to one embodiment of the present invention are combined ispreferably provided with a correction circuit having a function ofcorrecting a video signal with the use of artificial intelligence (AI).Specifically, learning by an artificial neural network (ANN) enables acorrection circuit to correct a video signal so as to alleviate thediscontinuity of the video particularly at the seam of the displayregion. Inference (recognition) is made by the artificial neural networkafter the learning, whereby a video signal is corrected to compensatefor discontinuity of the video. This makes it possible to display whatis called seamless video in which a seam is inconspicuous, so that thequality of high-resolution video can be improved.

Note that artificial intelligence refers to a computer that imitates theintelligence of human beings. An artificial neural network is a circuitthat imitates a neural network composed of neurons and synapses, and isa kind of artificial intelligence. In this specification and the like,the term “neural network” particularly refers to an artificial neuralnetwork.

With the use of artificial intelligence, the behavior can be analyzedand utilized efficiently and a subsequent operation can be determined.The repeated operation or information is stored as an experience pointthat serves as a standard of regularity recognition. General regularitycan be predicted from a large amount of data thus accumulated.

For example, environment data is used to integrate data. Data isintegrated by collecting a variety of information by various sensors, sothat prediction that is more effective than prediction with single datacan be made. For example, digital map data, data obtained from a camera,and positional information obtained wirelessly can be given.

In the case where a car driver parks a car in a parking lot, the drivingof the driver can be effectively assisted by hierarchical ordered set,utilizing data obtained from a camera, map data, and the like.Alternatively, when a driver switches the driving mode to an automaticdriving mode, the car utilizes artificial intelligence and data (a backmonitor, a lane tracking camera, and the like) and can stop at apredetermined position in a parking lot.

A large-sized flexible display panel has a problem in yield in aseparation process of a glass substrate; therefore, in many cases, usinga plurality of panels of the same size can reduce the manufacturingcost. That is, in consideration of cost and yield per large-sizedhigh-resolution panel, defects are more likely to occur as the areaseparated at a time gets larger, and, in some cases, the cost of a panelthat is manufactured by combining four panels of one-quarter size getslower, for example. In the case where a plurality of display panels thesizes of which are the same as that of a display device using a displaypanel of a given size are combined, depending on a factory manufacturingthe display panel, the manufacturing cost of photomasks can be reducedbecause the photomasks which are the same as those of the display panelof the given size can be used.

Alternatively, even for display regions having the same areas, aplurality of display panels whose terminal portions are provided indifferent positions may be combined. In the above structure, one featureis that a first terminal portion is included on a short side of thefirst display panel, the position of a second terminal portion isincluded on a long side of the second display panel, and the connectionposition of a first external terminal connected to the first terminalportion and the connection position of a second external terminalconnected to the second terminal portion are different from each other.The variation of the placement of the display panels can be increased bychanging the placement of the terminal portions.

Recently, there has been a movement to computerize a side mirror (alsoreferred to as a door mirror). An attempt to visualize the shot video inan in-car panel by providing a camera or a sensor as well as a sidemirror has been made. Moreover, it is said that a car will dispense witha side mirror that protrudes outside in the future. A side mirror hasconventionally been made to adjust its position in accordance with adriver's eye level and the position has been adjusted as appropriate;however, in the case where a side mirror is not provided andcomputerized, the adjustment is difficult. This is because a displaypanel on which video is displayed is fixed often, in which case an imagemight be difficult to see, and therefore there has been a problem insafety.

Thus, a state where an image is easily seen can be made in such a mannerthat one screen is formed by overlapping a plurality of display panelsand the driver curves part of the display panel as appropriate. That is,by curving part of the display panel, the driver can see the displaypanel easily. The in-car design can also be varied. In the case where acamera detects a rapidly approaching vehicle to which attention is to bepaid, part of the display panel may be automatically curved to drawattention so that the video display on which the vehicle is displayedmay urge the driver to recognize. Curving part of the display panel willshorten the distance from the driver; therefore, it is possible todisplay information that the driver having poor eyesight can easily see.

According to another embodiment of the present invention, in the abovestructure, one feature is that the first display panel or the seconddisplay panel has flexibility and has a position adjustment function ofcurving the end portion. The position adjustment function of curving theend portion of the display panel is provided with a member with whichthe periphery of the end portion is changed into a protruded state onthe rear side of the display panel, and the member may be mechanical ormanual one. According to another embodiment of the present invention,which is not limited to the use of a plurality of display panels, adisplay device includes a display panel having an organic light-emittingelement over a flexible film; an optical film over the display panel;and below an overlap between the optical film and the flexible film, aposition adjustment jig curving an end portion of the display panel; andboth the optical film and the flexible film are curved by a drivingmechanism of the position adjustment jig of curving the end portion ofthe display panel. Note that the optical film and the flexible film,whose materials are different from each other, are preferably not fixedto each other with an adhesive because the end portions of the differentfilms are shifted and the entire end portion of the display panel can becurved smoothly. Curving the end portion of the display panel anddisplaying video corresponding to a side mirror in the curved region candisplay information that a driver can easily see. For example, drivingthe position adjustment jig in synchronization with the operation of adirection indicator by a driver to curve the end portion of the displaypanel can assist driving by displaying the side mirror video on thecurved region as well as drawing driver's attention.

Note that the display device in which a plurality of display panels arecombined can be applied to the periphery of a driver's seat (alsoreferred to as a cockpit portion) of various kinds of vehicles such as alarge-sized vehicle, a middle-sized vehicle, and a small-sized vehicle(including a motorcycle). In addition, application to the periphery of adriver's seat of a vehicle such as an aircraft or a vessel is alsopossible.

The display device in which a plurality of display panels are combinedcan be incorporated along a surface including a curved surface of theinner wall (including a seat and a ceiling) of a car without beinglimited to the cockpit portion in the periphery of a driver's seat.

The display device in which a plurality of display panels are combinedcan also be applied to an automatic driving vehicle in which a driver (apilot or an operator such as a crewmember) can switches the driving modeto an automatic driving mode.

In the case of the automatic driving vehicle, the driving mode isswitched automatically when a sensor or the like detects whether a handcontacts with a handle or not or switched by a driver's input operation.For safety's sake, it is preferable to make a clear difference by videodisplay so that a driver can know exactly whether the vehicle is inautomatic driving or not. Therefore, it is preferable that the displaybe performed in a large area so that not only a driver but all of themembers that get in the vehicle can see and recognize switching displayof automatic driving even when they face whichever direction.

In the case of switching the driving mode from automatic driving tomanual driving, driving mode is switched when a driver recognizessetting or the like in automatic driving; therefore, more informationcan be obtained as a display region displaying such information getslarger.

In addition, display under strong external light in the daytime anddisplay in night are quantitatively different from each other bycomparison and how a driver sees the display is likely to change. Evenwhen the environment outside the vehicle is changed, a state where animage is easily seen can be obtained in such a manner that one screen isformed by overlapping a plurality of display panels and part of thedisplay panel is curved as appropriate by a driver. That is, by curvingpart of the display panel, the driver can see the display panel easily.

According to one embodiment of the present invention, a display deviceis not limited to being installed inside a vehicle. In some cases, adriver performs operation wirelessly from outside a remote-led car by aremote operation. Switching between automatic driving and a remoteoperation might also be possible. In that case, a driver's seat isprovided indoors, for example, at home; a display device of oneembodiment of the present invention is placed in the periphery of thedriver's seat; video shot by a camera provided in the remote-led car isdisplayed; and a driver performs a remote operation in the needed placeusing the video and automatic driving is performed in other places. Itis preferable to employ a high-resolution display panel using an organicEL element in the case where the landscape seen from the driver's seatover a windshield is displayed in video. Particularly at high-speeddriving, a vivid moving image in accordance with driving speed, on whichexternal environment that changes in accordance with the driving speedis displayed, is required. The response speed of the organic EL elementis remarkably higher than that of a liquid crystal display element;therefore, appropriate information can be provided and informationalmost in real time can be provided for a driver. Because the displaydevice in which a plurality of display panels are combined uses videodata independently, it is suitable for compressing each of the data andtransmitting and receiving the data wirelessly.

Effect of the Invention

Driver's safe driving can be ensured by providing a display region witha large area for a user such as a driver and using information displayedon the display region with a large area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Top views and cross-sectional views illustrating one embodimentof the present invention.

FIG. 2 A diagram illustrating an example of installing a display deviceof one embodiment of the present invention to a vehicle.

FIG. 3 Top views illustrating one embodiment of the present invention.

FIG. 4 A top view illustrating one embodiment of the present invention.

FIG. 5 Cross-sectional views illustrating an example of a manufacturingmethod of a display panel.

FIG. 6 Cross-sectional views illustrating an example of a manufacturingmethod of a display panel.

FIG. 7 Top views and a cross-sectional view illustrating an example of adisplay panel.

FIG. 8 A cross-sectional view illustrating an example of a displaydevice.

FIG. 9 Cross-sectional views illustrating an example of a display panel.

FIG. 10 Diagrams illustrating a display panel and a display device ofExample 1.

FIG. 11 A cross-sectional view illustrating a display device of Example1.

FIG. 12 Photographs of a display device.

FIG. 13 A diagram illustrating a perspective view of a positionadjustment jig.

FIG. 14 Photographs of a display device.

FIG. 15 A perspective view illustrating an example of a display device.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowby referring to the drawings. However, the present invention is notlimited to the description below, and it is easily understood by thoseskilled in the art that modes and details disclosed herein can bemodified in various ways. Further, the present invention is notconstrued as being limited to description of the embodiments givenbelow.

Embodiment 1

In this embodiment, a structure example and an application example of adisplay device of one embodiment of the present invention will bedescribed with reference to drawing.

Structure Example 1

FIG. 1(A) is a schematic top view of a display panel 100 included in adisplay device of one embodiment of the present invention.

The display panel 100 includes a display region 101 and avisible-light-transmitting region 110 and is adjacent to the displayregion 101. An example in which the display panel 100 is provided withan FPC (Flexible Printed Circuit) 112 which is a kind of externalterminal is illustrated in FIG. 1(A).

The display region 101 includes a plurality of pixels arranged in amatrix and can display an image. One or more display elements areprovided in each pixel. As the display element, typically, alight-emitting element such as an organic EL element, a liquid crystalelement, or the like can be used.

In the region 110, for example, a pair of substrates included in thedisplay panel 100, a sealant for sealing the display element sandwichedbetween the pair of substrates, and the like may be provided. Here, formembers provided in the region 110, materials having avisible-light-transmitting property are used. The region 110, in whichno wiring, element, or the like is provided except for the substrate andthe sealant, is a visible-light-transmitting region.

Here, the width W of the region 110 in FIG. 1(A) is preferably greaterthan or equal to 0.5 mm and less than or equal to 150 mm, furtherpreferably greater than or equal to 1 mm and less than or equal to 100mm, still further preferably greater than or equal to 2 mm and less thanor equal to 50 mm. The region 110 functions as a sealing region, and asthe width W of the region 110 becomes larger, the distance between anend surface of the display panel 100 and the display region 101 canbecome longer; therefore, entry of an impurity such as water into thedisplay region 101 from the outside can be effectively suppressed. Inparticular, in this structure example, the region 110 is providedadjacent to the display region 101; thus, it is important to set thewidth W of the region 110 at an appropriate value. For example, in thecase where an organic EL element is used as the display element, thewidth W of the region 110 is set to be greater than or equal to 1 mm,whereby deterioration of the EL element can be effectively suppressed.Note that also in a portion other than the region 110, the distancebetween the end portion of the display region 101 and the end surface ofthe display panel 100 is preferably set to be in the above range.

In a region 120, for example, a wiring electrically connected to thepixels included in the display region 101 is provided. In addition tosuch a wiring, driver circuits for driving the pixels (such as a scanline driver circuit and a signal line driver circuit) may be provided.Furthermore, the region 120 includes a region provided with a terminalelectrically connected to the FPC 112 (also referred to as a connectionterminal), a wiring electrically connected to the terminal, an IC chip,and the like.

A display device 10 of one embodiment of the present invention includesa plurality of the above display panels 100. FIG. 1(B) is a schematictop view of the display device 10 including three display panels 100 a,100 b, and 100 c.

Note that hereinafter, to distinguish the display panels from eachother, the same components included in the display panels from eachother, or the same components relating to the display panels from eachother, alphabets are added after reference numerals. Unless otherwisespecified, “a” is added to a display panel and components placed on thelowest side (the side opposite to the display surface side), and to oneor more display panels and components sequentially placed thereover,alphabets are added in alphabetical order after reference numerals.Unless otherwise specified, in describing a structure in which aplurality of display panels is included, alphabets are not added when acommon part of the display panels or the components is described.

The display device 10 illustrated in FIG. 1(B) is provided with adisplay region 101 a, a display region 101 b, and a display region 101c, and includes one optical film (typically circular polarizing film)overlapping with all of these display regions. Although optical filmscan be separately attached, in that case, steps are generated and aboundary is likely to be noticed when an optical film overlaps with anadjacent panel. In the case where optical films are separately attached,maximum three optical films overlap with one another. It is preferablethat one optical film be used in common and three display panels beplaced to overlap partly with the optical film because overlappingportions are reduced and the surface seems flat. Note that in FIG. 1(B),a portion 163 is a place where the three display panels overlap with oneanother.

The display panel 100 b is placed partly overlapping with an upper side(a display surface side) of the display panel 100 a. Specifically, avisible-light-transmitting region 110 b of the display panel 100 b isplaced to overlap with the display region 101 a of the display panel 100a.

In a portion 161, a visible-light-transmitting region 110 a of thedisplay panel 100 a placed on the lower side overlaps with the displayregion 101 b of the display panel 100 b placed on the upper side. In aportion 162, the display region 101 c of the display panel 100 c placedon the lower side overlaps with the visible-light-transmitting region110 b of the display panel 100 b placed on the upper side.

The display panel 100 c is placed partly overlapping with a lower side(a rear surface side) of the display panel 1006. Specifically, avisible-light-transmitting region 110 c of the display panel 100 c isplaced to overlap with the display region 101 b of the display panel 100b, and an FPC of the display panel 100 c is placed to overlap with thedisplay region 101 b of the display panel 100 b.

The visible-light-transmitting region 110 b overlaps the display region101 a; thus, the whole display region 101 a can be visually seen fromthe display surface side. The visible-light-transmitting regions 110 aand 110 b overlap the display region 101 c; thus, the whole displayregion 101 c can be visually seen from the display surface side. Aregion where the display region 101 a, the display region 101 b, and thedisplay region 101 c are placed so that a seam is inconspicuous canserve as one display region of the display device 10. The one displayregion of the display device 10 has a substantially T-shape asillustrated in FIG. 1(B).

FIG. 1(B) illustrates the case where the same display panel 100 is usedfor all the three display panels.

A schematic diagram of the display device 10 taken along a chain line ABin FIG. 1(B) is illustrated in FIG. 1(C). Note that in FIG. 1(C), foreasy understanding, the display region 101 a, the display region 101 c,the region 110 b, a region 120 b, and a region 120 c are illustrated toinclude a film to be a base.

The display device 10 has a structure in which an optical member 166 isplaced on the outermost surface.

The optical member 166 is provided in contact with at least the displayregion 101 b, FIG. 1(C) illustrates an example in which the opticalmember 166 overlaps with the entire areas of the display panels. Theoptical member 166 and each of the display panels may be fixed at leastpartly with an adhesive or the like, or may not be fixed at all. Forexample, the optical member 166 and each of the display panels may beindependently fixed to the display device 10 or a housing included in anelectronic device.

As the optical member 166, one or more of a polarizing member, aretardation member, an anti-reflection member, and the like can be usedin an overlapping state. Moreover, hard coat treatment may be performedon the outermost surface of the optical member 166.

Examples of the polarizing member include a polarizing plate and apolarizing film.

Examples of the retardation member include a retardation plate and aretardation film.

Examples of the anti-reflection member include an anti-reflection film(also referred to as AR film), a low-reflection film (also referred toas LR film), and an anti-glare film (also referred to as AG film ornon-glare film). Furthermore, an anti-reflection plate and ananti-reflection film that each have the same function as that of any ofthese films are also examples of the anti-reflection member.

In this embodiment, an example in which a circularly polarizing plate isused as the optical member 166 is described. The circularly polarizingplate includes a linear polarizing plate and a retardation plate. Thelinear polarizing plate includes, for example, a linear polarizing layerbetween a pair of substrates. An example of a retardation plate includesa 1/4 λplate. The linear polarizing plate and the retardation plate areattached to each other with a bonding layer. With the use of thecircularly polarizing plate, a user of the display device can beprevented from seeing an overlapping area because of the reflection oflight at surfaces and the inside of the display panels.

A portion 165 illustrated in FIG. 1(B) is a deformation place. Aschematic diagram of the display device 10 taken along a chain line CDin FIG. 1(B) is illustrated in FIG. 1(D).

When the end portion of the display region 101 b is push by a positionadjustment unit 167, part of the display region 101 b is curved andbecomes the portion 165 which is deformed in a protruded state. Bycurving part of the display panel, it can be easily seen. The design ofthe display device 10 can also be varied.

In the case of moving the position adjustment unit 167, the opticalmember 166 and the display panel are preferably not fixed with anadhesive or the like. In the case where the position adjustment unit 167is moved to curve the display panel, the display panel can be curvedmore smoothly when the optical member 166 and the display panel are notbonded to each other. The position adjustment unit 167 includes a motor,a jig, a hinge, and the like.

Embodiment 2

In this embodiment, application examples in which the display devicedescribed in the above embodiment is placed in a vehicle will bedescribed below.

FIG. 2 illustrates an example of installing a display device 5002 to aright-hand vehicle, but there is no particular limitation. In the caseof a left-hand vehicle, the placement of the left and right is replaced.

FIG. 2 illustrates a dashboard 5001, a handle 5003, a windshield 5004,and the like which are placed around a driver's seat and a frontpassenger's seat.

The display device 5002 is placed in a predetermined position in thedashboard 5001, specifically, around the driver, and has a substantialT-shape. The substantial T-shape is preferable because a display regioncan be provided in front of the driver's seat, in front of the frontpassenger's seat, and between the driver's seat and the frontpassenger's seat in the car. FIG. 2 illustrates an example in which aplurality of display panels are combined into one display device 5002 onthe curved surface of the dashboard 5001; however, the number of displaydevices is not limited to one, and a plurality of display devices may beprovided separately in a plurality of places. The one display device5002 illustrated in FIG. 2 has a complex shape which includes aplurality of openings and does not include display regions in a handleconnection portion, a display portion of a meter, a ventilation duct5006, and the like. Achieving such a complex shape is one of theadvantages of using a flexible display panel.

A plurality of cameras 5005 for shooting the situation on the rear sideare provided outside the car. Although the camera 5005 is providedinstead of a side mirror in the example of FIG. 2, both the side mirrorand the camera for shooting the situation of the rear side may beprovided.

The camera 5005 can be a CCD camera or a CMOS camera, or an infraredcamera may be combined to them. The infrared camera can detect orextract a living body such as a human or an animal because as thetemperature of the object increases, the output level increases.

An image taken with the camera 5005 can be output to the screen of thedisplay device 5002 one or a plurality of display regions 5002 a, 5002b, 5002 c, and 5002 d). Note that the display device 5002, in which, forexample, the display region 5002 a corresponds to one display panel, isbroadly composed of four display panels.

This display device 5002 is mainly used for drive support. The situationon the rear side is shot at a wide angle of view in the horizontaldirection by the camera 5005, and the image is displayed so that thedriver can see a blind area to avoid an accident.

For the display regions 5002 a, 5002 b, 5002 c, and 5002 d, the use of adisplay system including a correction circuit having a function ofcorrecting a video signal using artificial intelligence (AI) ispreferably used to display a video in which a seam between videos ofadjacent display regions is inconspicuous. Specifically, a correctioncircuit capable of correcting a video signal so that discontinuity ofthe video particularly at the seam between the regions can be relievedby learning of an artificial neural network (ANN) is used. Inference(recognition) is made by the artificial neural network after thelearning, whereby a video signal is corrected to compensate fordiscontinuity of a video. This makes it possible to display the video inwhich a seam is inconspicuous, so that the quality of a high-resolutionvideo can be improved.

Since the display region 5002 d of the display device 5002 is flexible,the angle of a screen that is part of the display region 5002 d can bechanged to an angle easy for the driver to see by curving a left-edgeportion 5002 e using a position adjustment unit. It is hard to recognizedisplay of the edge of the display region 5002 d due to the distance andviewing angle from the driver; however, when the left-edge portion 5002e of the display region 5002 d is curved to have an angle the driver caneasily see, the edge of the display region 5002 d can be provided at aposition suitable for a display region where an image of a side mirroris displayed in the car, which is useful.

A distance image sensor may be provided over a roof or the like of thecar to display an obtained image on the display device 5002. As thedistance image sensor, an image sensor or a LIDAR (Light Detection andRanging) is used. When an image obtained by a distance image sensor andan image obtained by a CCD camera are displayed on a display devicewhose display area is large, more information can be provided to thedriver to support the driving.

When the display device 5002 also displays map information, trafficinformation, a television picture, a DVD picture, and the like, moredisplay panels are preferably combined to increase the display area ofthe display device. For example, map information can be displayedlargely on the display regions 5002 a, 5002 b, 5002 c, and 5002 d as onedisplay screen.

In the display regions 5002 a, 5002 b, 5002 c, and 5002 d, the regionsdisplaying video are not fixed and can be freely changed to meet thedriver's preference. For example, a television picture and a DVD picturecan be displayed in the display region 5002 d on the left, mapinformation can be displayed in the display region 5002 b at the centerposition, meters can be displayed in the display region 5002 c on theright, and audio information can be displayed in the display region 5002a near a transmission gear between the driver's seat and the frontpassenger's seat. Owing to the combination of a plurality of displaypanels, a fail-safe design can be achieved. For example, even when onedisplay panel in a display region composed of a plurality of displaypanels is broken for any reason, display regions to be used can beswitched so that a display panel in another region can alternatively beused.

In the case of a flat display panel, the installation place is limitedand there is dead space between the display panel and a curved surfaceof the interior car body, so that the in-car space is narrowed. Thedisplay panels used for the display regions 5002 a, 5002 b, 5002 c, and5002 d are desirably flexible display panels because the display panelscan be installed along the curved surface of the interior car body andtherefore the in-car space is hardly narrowed. Note that a flat displaypanel may be provided in combination with a flexible display panel aslong as the in-car space is not narrowed so much. For example, thedisplay radon 5002 a may be a flat display panel. Alternatively, thedisplay region 5002 a, which is a region that the driver can reach, maybe a touch panel so that input operation can be performed.

Although the example in which the display panel is applied to adashboard of a vehicle is described in this embodiment, one embodimentof the present invention is not particularly limited and, for example,an example of a motorcycle such as a motor scooter is illustrated inFIG. 15.

The display device 8605 is placed near a driver's front handlebar,specifically, around the driver, and has a substantial T-shape. Thedisplay device 8605 is composed of three display panels and can performdisplay by switching between speed meter display, navigation display,back monitor display, and the like as appropriate.

Moreover, the display device of this embodiment can also be used as adisplay device in a cockpit of an aircraft. Alternatively, the displaydevice of this embodiment can be provided in a micro mobility, which isa kind of electric vehicle.

A motor scooter 8600 illustrated in FIG. 15 includes a display device8605, a power storage device 8602, side mirrors 8601, and indicators8603. The power storage device 8602 stored in a trunk 8604 can supplyelectric power to the display device 8605 and the direction indicators8603.

For another example, the display device of this embodiment may be usedfor a boarding-type mobile assistive robot that has a plane to put thefoot between the two wheels and moves by passenger's movement of thecenter of gravity and the like.

Alternatively, the display device of this embodiment can also be used asa display device for digital signage mounted on a structure such as acylindrical column. The display device of this embodiment can also beincorporated along a curved surface of the inner wall or the outer wallof a house or a building.

This embodiment can be freely combined with Embodiment 1.

Embodiment 3

Although the same display panel 100 is used for all of the three displaypanels in FIG. 1(B) shown in Embodiment 1, FIG. 3 illustrates an exampleof using a partly different display panel in this embodiment. Note thatthe display panel in this embodiment is different only partly and theportions in FIG. 3 which are the same as those in FIG. 1 are denoted bythe same reference numerals.

FIG. 3(A) is a schematic top view of a display panel 100 d included in adisplay device of one embodiment of the present invention.

The display panel 100 d includes a display region 101 d, avisible-light-transmitting region 110 d that is adjacent to the displayregion 101 d, and a region 120 d. In FIG. 3(A), the region 120 d isprovided with an FPC 112 d that is a kind of external terminal. In thedisplay panel 100 d, the area of the display region 101 d is almost thesame area as that of the display region 101 of the display panel 100illustrated in FIG. 1(A), but the position of the region 120, where theFPC is provided, is different.

In a display device 11 of one embodiment of the present invention, threedisplay panels are combined in total: two display panels 100 illustratedin FIG. 1(A) and one display panel 100 d illustrated in FIG. 3(A). FIG.3(B) shows a schematic top view of the display device 11 including thethree display panels 100 a, 100 c, and 100 d.

In the display device 11 illustrated in FIG. 3(B), the display region101 a, the display region 101 c, and the display region 101 d are placedalmost without a space therebetween, and one optical film (typicallycircular polarizing film) overlapping with all of these display regionsis provided. Note that in FIG. 1(B), the portion 163 is a place wherethe three display panels overlap with one another.

The display panel 100 d is placed partly overlapping with a lower sideof the display panel 100 a. Specifically, the display region 101 a ofthe display panel 100 a is placed on the upper side and placed so thatthe region 120 d and the FTC 112 d of the display panel 100 d overlapwith the region 110 a. The place where the visible-light-transmittingregion 110 a of the display panel 100 a provided on the upper side andthe display panel 100 d provided on the lower side overlap with eachother is illustrated as a portion 168. An image is displayed on theportion 168 of the display panel 100 d with light transmitted from theregion 110 a.

Although the region 120 including a portion connected to the ITC can bedeformed as compared with the display region 101, it is difficult insome cases to deform repeatedly. In FIG. 3(B), the display panel 100 dis used instead of the display panel 100 b in FIG. 1(B), so that thearea of the portion 165 to be a deformation place can be increased. Byan increase in the area of the portion 165, the display panel can bedeformed so that a driver and the like can see more image information ata position that can be easily seen. Particularly the hood of a largevehicle such as a truck is wide and a display panel can be provided upto a place far from a driver; therefore, it is useful to deform part ofthe display panel at a far place to be seen easily.

FIG. 3(C) is illustrated as a modification example of FIG. 3(B). FIG.3(C) illustrates a display device 12 further combined with a displaypanel 100 f. One display region in the display device 12 is the sum ofthe display region 101 a, the display region 101 d, the display region101 c, and a display region 101 f. In this specification, the shape ofsuch one display region is referred to as a T-shape. In FIG. 3(C), theportion 165 to be a deformation place can be provided on both sides ofthe display device 12.

FIG. 4 is illustrated as a modification example of FIG. 3(B). FIG. 4illustrates a display device 13 in which the three display panels 100 dare arranged transversely and two display panels 100 e and 100 g arearranged longitudinally. One display region in the display device 13 isthe sum of the three display regions 101 d, a display region 101 e, anda display region 101 g. In this specification, the shape of such onedisplay region is referred to as a T-shape. The T-shape is a kind ofshape in which a longitudinal bar portion and a lateral bar portion arecombined, which is formed at substantially 90°, so that long-axisdirections intersect with each other. The T-shape is not limited to theshape in which the two bars are made in contact with each other near thecenter of the lateral bar, i.e. a symmetrical shape.

In addition, in FIG. 4, the three display panels are placed so as not tooverlap with one another, and the display device 13 does not include aportion where the three display panels overlap with one another.Although not illustrated, an FPC of the display panel 100 e is placed ina position overlapping with the display panel 100 d.

In addition, in the three display panels 100 d of the display device 13which are arranged, the left panel in FIG. 4 is placed in the uppermostpart, the right panel is placed in the lowermost part, and an FPC of theMiddle panel is placed so as to overlap with the display region of theleft display panel.

In FIG. 4, the display panel 100 e may have a shape with a curvedsurface, and the display panel 100 g may be a liquid crystal displaydevice using a conventional glass substrate. In this case, the displaysurface of the display panel 100 d can be curved at an angle greaterthan or equal to 60° and less than or equal to 120° with respect to theflat plane of the display panel.

A display device including a display region with a large area can beprovided by such a variety of combinations. The display devices can becombined as appropriate along a cockpit of a car, an aircraft, or avessel.

This embodiment can be freely combined with the other embodiments.

Embodiment 4

In this embodiment, a manufacturing method of the display panel of oneembodiment of the present invention illustrated in FIG. 1(A) will bedescribed with reference to FIG. 5.

First, as illustrated in FIG. 5(A), a separation layer 233 is formedover a formation substrate 231. Then, plasma treatment is performed on asurface of the separation layer 233 (see the arrows indicated by dottedlines in FIG. 5(A)). Note that in this specification, a layer formedover a separation layer may be referred to as a layer to be separated.

As the formation substrate 231, a substrate having heat resistance highenough to withstand at least process temperature in a manufacturingprocess is used. As the formation substrate 231, for example, a glasssubstrate, a quartz substrate, a sapphire substrate, a semiconductorsubstrate, a ceramic substrate, a metal substrate, or a plasticsubstrate can be used.

Note that it is preferable to use a large-sized glass substrate as theformation substrate 231 in order to improve mass productivity. Forexample, a glass substrate having a size greater than or equal to the3rd generation (550 mm×650 mm) and less than or equal to the 10thgeneration (2950 mm×3400 mm) or a glass substrate having a larger sizethan this is preferably used.

In the case where a glass substrate is used as the formation substrate231, a base film is preferably formed between the formation substrate231 and the separation layer 233 because contamination from the glasssubstrate can be prevented. Examples of the base film include insulatingfilms such as a silicon oxide film, a silicon oxynitride film, a siliconnitride film, and a silicon nitride oxide film.

As the separation layer 233, an inorganic material can be used. Examplesof the inorganic material include a metal, an alloy, a compound, and thelike that contain an element selected from tungsten, molybdenum,titanium, tantalum, niobium, nickel, cobalt, zirconium, zinc, ruthenium,rhodium, palladium, osmium, iridium, and silicon. A crystal structure ofa layer containing silicon may be amorphous, microcrystal, orpolycrystal. A high-melting point metal material such as tungsten,titanium, or molybdenum is preferably used for the separation layer 233because the degree of freedom of the process for forming the layer to beseparated can be increased.

In the case where the separation layer 233 has a single-layer structure,a tungsten layer, a molybdenum layer, or a layer containing a mixture oftungsten and molybdenum is preferably formed. Note that the mixture oftungsten and molybdenum corresponds to an alloy of tungsten andmolybdenum, for example.

The separation layer 233 can be formed by, for example, a sputteringmethod, a CVD (Chemical Vapor Deposition) method (a plasma CVD method, athermal CVD method, a MOCVD (Metal Organic CVD) method, or the like), anALD (Atomic Layer Deposition) method, a coating method (including a spincoating method, a droplet discharge method, a dispensing method, or thelike), a printing method, or an evaporation method.

The thickness of the separation layer 233 is greater than or equal to 1nm and less than or equal to 1000 nm, preferably greater than or equalto 1 nm and less than or equal to 200 nm, further preferably greaterthan or equal to 10 nm and less than or equal to 100 nm.

In the case where, as the separation layer 233, a stacked-layerstructure of a layer containing tungsten and a layer containing an oxideof tungsten is formed, the following manner may be utilized: the layercontaining tungsten is formed and an oxide insulating film is formedthereover, so that the layer containing an oxide of tungsten is formedat the interface between the tungsten layer and the insulating film.

Alternatively, the layer containing an oxide of tungsten may be formedby performing thermal oxidation treatment, oxygen plasma treatment,nitrous oxide (N₂O) plasma treatment, treatment with a highly oxidizingsolution such as ozone water, or the like on the surface of the layercontaining tungsten. Plasma treatment or heat treatment can be performedunder an atmosphere of oxygen, nitrogen, or nitrous oxide alone, or amixed gas of any of these gasses and another gas.

Surface condition of the separation layer 233 is changed by the plasmatreatment or heat treatment, whereby adhesion between the separationlayer 233 and the insulating film formed later can be controlled. Inthis embodiment, the case where plasma treatment is performed will bedescribed as an example.

The plasma treatment is preferably performed under an atmospherecontaining nitrous oxide, further preferably under an atmospherecontaining nitrous oxide and silane. Thus, an oxide layer of a materialincluded in the separation layer 233 can be formed on the surface of theseparation layer 233. In particular, when the plasma treatment isperformed under an atmosphere containing silane, an oxide layer with anextremely small thickness can be formed. When having an extremely smallthickness, the oxide layer is difficult to observe in a cross-sectionalobservation image.

The oxide layer is a layer containing an oxide of the material includedin the separation layer. In the case where a metal is contained in theseparation layer 233, the oxide layer is a layer containing an oxide ofthe metal contained in the separation layer 233. The oxide layerpreferably contains tungsten oxide, titanium oxide, or molybdenum oxide.

Next, as illustrated in FIG. 5(B), a first insulating layer 205 isformed over the separation layer 233, and a second insulating layer 207is formed over the first insulating layer 205.

Although the example in which the stacked-layer structure of the layercontaining tungsten and the layer containing an oxide of tungsten isused as the separation layer 233 is described in this embodiment,without particular limitation thereon, the following manner may beemployed: with the use of an organic resin such as polyimide, theorganic resin and the first insulating layer 205 are stacked over aformation substrate, and a separation trigger is formed by locallyheating part of the organic resin by laser light or the like, so thatseparation is performed at an interface between the formation substrateand the first insulating layer 205.

As each of the first insulating layer 205 and the second insulatinglayer 207, a single layer or a multilayer using a silicon nitride film,a silicon oxynitride film, a silicon oxide film, a silicon nitride oxidefilm, or the like can be formed.

Note that in this specification, “silicon oxynitride” contains moreoxygen than nitrogen in its composition. Moreover, in thisspecification, “silicon nitride oxide” contains more nitrogen thanoxygen in its composition.

The first insulating layer 205 preferably contains oxygen and silicon.The first insulating layer 205 preferably has a single-layer structureof a silicon oxide film or a silicon oxynitride film.

It is preferable that the first insulating layer 205 further containhydrogen. The first insulating layer 205 has a function of releasinghydrogen in a later heating step. Hydrogen is released from the firstinsulating layer 205 by heating, whereby hydrogen is supplied to theoxide layer. The first insulating layer 205 may further have a functionof releasing hydrogen and nitrogen in the later heating step. Whennitrogen is released from the first insulating layer 205 by heating,nitrogen is supplied to the oxide layer.

The first insulating layer 205 preferably includes a region in which thehydrogen concentration, which is detected by secondary ion massspectrometry (SIMS), is greater than or equal to 1.0×10²⁰ atoms/cm³ andless than or equal to 1.0×10 atoms/cm³, preferably greater than or equalto 5.0×10²⁰ atoms/cm³ and less than or equal to 5.0×10²¹ atoms/cm³.

The first insulating layer 205 preferably includes a region in which thenitrogen concentration, which is detected by SIMS, is greater than orequal to 5.0×10²⁰ atoms/cm³ and less than or equal to 1.0×10²³atoms/cm³, preferably greater than or equal to 1.0×10²¹ atoms/cm³ andless than or equal to 5.0×10²² atoms/cm³.

As the first insulating layer 205, a silicon oxide film or a siliconoxynitride film is preferably formed by a plasma CVD method using adeposition gas containing a silane gas and a nitrous oxide gas because alarge amount of hydrogen and nitrogen can be contained in the film. Inaddition, the proportion of the silane gas in the deposition gas ispreferably higher because the amount of released hydrogen in a laterheating step is increased.

The second insulating layer 207 preferably contains nitrogen andsilicon. The second insulating layer 207 preferably has a single-layerstructure of a silicon nitride film or a silicon nitride oxide film or astacked-layer structure including a silicon nitride film or a siliconnitride oxide film. In the case where the second insulating layer 207has a stacked-layer structure, the second insulating layer 207preferably further includes at least one of a silicon oxide film and asilicon oxynitride film.

The second insulating layer 207 has a function of blocking hydrogenreleased from the first insulating layer 205 in a later heating step.The second insulating layer 207 may be a layer that can block hydrogenand nitrogen. By the second insulating layer 207, supply of hydrogen(and nitrogen) from the first insulating layer 205 to an element layercan be suppressed and hydrogen (and nitrogen) can be supplied to theoxide layer efficiently. Note that another layer may be included betweenthe first insulating layer 205 and the second insulating layer 207.

A silicon nitride film included in the second insulating layer 207 ispreferably formed by a plasma CVD method using a deposition gascontaining a silane gas, a nitrogen gas, and an ammonia gas.

The first insulating layer 205 and the second insulating layer 207 caneach be formed by a sputtering method, a plasma. CVD method, a coatingmethod, a printing method, or the like, and can be a dense film havingan excellent moisture-resistant property by being formed at a depositiontemperature higher than or equal to 250° C. and lower than or equal to400° C. by a plasma CVD method, for example. Note that each thickness ofthe first insulating layer 205 and the second insulating layer 207 ispreferably greater than or equal to 10 nm and less than or equal to 3000nm, further preferably greater than or equal to 200 nm and less than orequal to 1500 nm.

Next, the separation layer 233, the first insulating layer 205, and thesecond insulating layer 207 are heated. Note that the heat treatment maybe performed after at least part of an element layer 209 described lateris formed. For example, the heat treatment may be performed after atransistor is formed and before the display element is formed. In thecase where a heating step is included in the manufacturing process ofthe element layer 209, the heating step may also serve as the heattreatment.

By performing the heat treatment, hydrogen (and nitrogen) is releasedfrom the first insulating layer 205 to be supplied to the oxide layer.At this time, the second insulating layer 207 blocks the releasedhydrogen (and nitrogen); thus, hydrogen (and nitrogen) can beefficiently supplied to the oxide layer.

The oxide in the oxide layer is reduced by hydrogen supplied to theoxide layer, so that a plurality of oxides with different proportions ofoxygen are mixed in the oxide layer. For example, in the case wheretungsten is contained in the separation layer, WO₃ formed by plasmatreatment is reduced to generate tungsten oxide WO_(x) (2<x<3) and WO₂with a proportion of oxygen lower than that of WO₃, leading to a statewhere these are mixed. Such a mixed metal oxide shows different crystalstructures depending on the proportion of oxygen; thus, the mechanicalstrength of the oxide layer is reduced. As a result, a state that islikely to be damaged is achieved inside the oxide layer, so that theseparability in a later separation process can be improved.

In addition, a compound containing a material contained in theseparation layer and nitrogen is also generated by nitrogen supplied tothe oxide layer. Existence of such a compound can further weaken themechanical strength of the oxide layer, so that the separability can beincreased. In the case where a metal is contained in the separationlayer, a compound containing the metal and nitrogen (a metal nitride) isgenerated in the oxide layer. For example, in the case where tungsten iscontained in the separation layer, tungsten nitride is generated in theoxide layer.

As the amount of hydrogen supplied to the oxide layer is larger, WO₃ ismore likely to be reduced and a state where a plurality of oxides withdifferent proportions of oxygen are mixed is more likely to be formed inthe oxide layer; therefore, the force required for the separation can bereduced. As the amount of nitrogen supplied to the oxide layer islarger, the mechanical strength of the oxide layer can be weakened andthe force required for the separation can be reduced. The thickness ofthe first insulating layer 205 is preferably larger because the amountof released hydrogen (and nitrogen) can be increased. On the other hand,the first insulating layer 205 preferably has a smaller thicknessbecause the productivity is increased.

The heat treatment may be performed at a temperature higher than orequal to the temperature at which hydrogen (and nitrogen) is desorbedfrom the first insulating layer 205 and lower than or equal to thetemperature at which the formation substrate 231 is softened. Theheating is preferably performed at a temperature higher than or equal tothe temperature at which the reduction reaction of the metal oxide inthe oxide layer with hydrogen occurs. The higher the temperature of theheat treatment is, the larger the amount of the hydrogen (and nitrogen)desorbed from the first insulating layer 205 is; thus, subsequentseparability can be improved. Note that depending on heating time andheating temperature, the separability may be so high that separation mayoccur at an unintended timing. Thus, in the case where tungsten is usedfor the separation layer 233, the heating is performed at a temperaturehigher than or equal to 300° C. and lower than 700° C., preferablyhigher than or equal to 400° C. and lower than 650° C., furtherpreferably higher than or equal to 400° C. and lower than or equal to500° C.

Although the atmosphere in which the heat treatment is performed is notparticularly limited and may be an air atmosphere, it is preferablyperformed in an inert gas atmosphere such as nitrogen or a rare gas.

Next, as illustrated in FIG. 5(C), the second insulating layer 207 inthe visible-light-transmitting region 110 is removed. A dry etchingmethod, a wet etching method, or the like can be used for the removal ofthe second insulating layer 207. Note that any of etching steps includedin later manufacturing processes of the element layer 209 or the likemay also serve as the removal step of the second insulating layer 207.

In one embodiment of the present invention, the second insulating layer207 is provided over the entire surface of the separation layer 233until the heat treatment is performed. Then, after the heat treatment,the second insulating layer 207 in the visible-light-transmitting region110 is removed. Accordingly, the separability in thevisible-light-transmitting region 110 can be prevented from being lowerthan that in the other region. Thus, the separability of the entiredisplay panel can be uniform. An influence of the structure of thevisible-light-transmitting region 110 on the yield of the manufacturingprocess of the display panel can be reduced.

Next, as illustrated in FIG. 5(D), the element layer 209 and aconnection terminal 223 are formed over the second insulating layer 207.The display element is included in the element layer 209. It ispreferable that an insulating layer included in the element layer 209 benot included in the visible-light-transmitting region 110.

Next, a substrate 235 attached to the formation substrate 231 in a laterstep is prepared. A separation layer 237 is formed over the substrate235. Then, plasma treatment is performed on a surface of the separationlayer 237 (see the arrows indicated by dotted lines in FIG. 5(E)).

Next, as illustrated in FIG. 5(F), a third insulating layer 215 isformed over the separation layer 237, a fourth insulating layer 217 isformed over the third insulating layer 215, and a functional layer 219is formed over the fourth insulating layer 217.

Note that heat treatment is performed after the fourth insulating layer217 is formed and before part of the fourth insulating layer 217 isremoved. The separation layer 237, the third insulating layer 215, andthe fourth insulating layer 217 may be heated before the functionallayer 219 is formed. Alternatively, the heat treatment may be performedafter at least part of the functional layer 219 is formed. In the casewhere a heating step is included in the manufacturing process of thefunctional layer 219, the heating step may also serve as the heattreatment.

By performing the heat treatment, the separability in a later separationprocess can be improved.

Next, as illustrated in FIG. 5(G), the fourth insulating layer 217 inthe visible-light-transmitting region 110 is removed. A dry etchingmethod, a wet etching, or the like can be used for the removal of thefourth insulating layer 217. Note that any of etching steps included inthe manufacturing process of the functional layer 219 may also serve asthe removal step of the fourth insulating layer 217.

In one embodiment of the present invention, the fourth insulating layer217 is provided over the entire surface of the separation layer 237until the heat treatment is performed. Then, after the heat treatment,the fourth insulating layer 217 in the visible-light-transmitting region110 is removed. Accordingly, the separability of the entire displaypanel can be uniform. An influence of the structure of thevisible-light-transmitting region 110 on the yield of the manufacturingprocess of the display panel can be reduced.

Next, the formation substrate 231 and the substrate 235 are attached toeach other with a bonding layer 221 (see FIG. 6(A)).

As the bonding layer 221, a variety of curable adhesives such as aphotocurable adhesive such as an ultraviolet curable adhesive, areactive curable adhesive, a thermosetting adhesive, and an anaerobicadhesive can be used. Alternatively, as the bonding layer 221, anadhesive with which the substrate 235 and the first insulating layer 205can be separated from each other when necessary, such as a water-solubleresin, a resin soluble in an organic solvent, or a resin which iscapable of being plasticized upon irradiation with UV light, may beused.

Then, the separation layer 233 and the first insulating layer 205 areseparated from each other.

As the separation method, for example, the formation substrate 231 orthe substrate 235 is fixed to a suction stage and a separation startingpoint is formed between the separation layer 233 and the firstinsulating layer 205. The separation starting point may be formed by,for example, inserting a sharp instrument such as a knife between them.Alternatively, the separation starting point may be formed by meltingpart of the separation layer 233 by irradiation with laser light.Alternatively, the separation starting point may be formed by drippingliquid (e.g., alcohol, water, or water containing carbon dioxide) ontoan end portion of, for example, the separation layer 233 or the firstinsulating layer 205 so that the liquid penetrates into an interfacebetween the separation layer 233 and the first insulating layer 205 byusing capillary action.

Then, physical force (a separation process with a human hand or with ajig, a separation process by rotation of a roller, or the like) isgently applied to the area where the separation starting point is formedin a direction substantially perpendicular to the bonded surfaces, sothat separation can be caused without damage to the layer to beseparated. For example, separation may be caused by attaching tape orthe like to the formation substrate 231 or the substrate 235 and pullingthe tape in the aforementioned direction, or separation may be caused bypulling an end portion of the formation substrate 231 or the substrate235 with a hook-like member. Alternatively, separation may be caused byadsorbing an adhesive member or a member capable of vacuum suction onthe rear side of the formation substrate 231 or the substrate 235 andpulling it up.

Here, separation is caused in such a manner that liquid containing watersuch as water or an aqueous solution is added to the separationinterface at separation and the liquid penetrates into the separationinterface, so that the separability can be improved. Furthermore, anadverse influence of static electricity caused at separation on thefunctional element included in the layer to be separated (breakdown of asemiconductor element by static electricity, or the like) can bereduced.

By the above method, the layer to be separated can be separated from theformation substrate 231 with a high yield.

After that, a substrate 201 is attached to the first insulating layer205 with a bonding layer 203 therebetween (FIG. 6(B)). For the bondinglayer 203, a material that can be used for the bonding layer 221 can beused. For the substrate 201, a material that can be used for a substrate211 described later can be used.

Next, the separation layer 237 and the substrate 235 are separated.

After that, the substrate 211 is attached to the first insulating layer215 with a bonding layer 213 therebetween (FIG. 6(C)).

As the substrate 211, various substrates that can be used as theformation substrate 231 can be used. Alternatively, a substrate havingflexibility may be used. Alternatively, as the substrate 211, asubstrate provided in advance with a functional element such as asemiconductor element such as a transistor, a light-emitting elementsuch as an organic EL element, a liquid crystal element, or a sensingelement, a color filter, and the like may be used. For the bonding layer213, a material that can be used for the bonding layer 221 can be used.

By using substrate having flexibility as the substrate 201 and thesubstrate 211, a flexible display panel can be fabricated. Note that inthe case where the substrate 211 functions as a temporary supportingsubstrate, the substrate 211 and the layer to be separated are separatedfrom each other, and the layer to be separated may be attached toanother substrate (e.g., a substrate having flexibility).

As described above, in the manufacturing method of a display panel ofone embodiment of the present invention, the heat treatment is performedwhile the first insulating layer 205 and the second insulating layer 207are formed over the entire surface of the separation layer 233; thus,the separability of the entire display panel can be uniformly increased.Furthermore, the second insulating layer 207 in thevisible-light-transmitting region 110 is removed after the heattreatment, so that the reflectance in the visible-light-transmittingregion 110 can be reduced.

Moreover, in the manufacturing method of a display panel of oneembodiment of the present invention, a functional element is formed overa formation substrate, separated from the formation substrate, and thentransferred to another substrate. Thus, there is almost no limitation onthe temperature applied in formation steps of a functional element. Afunctional element with extremely high reliability that is manufacturedthrough a high-temperature process can be manufactured with a high yieldover a substrate having flexibility with poor heat resistance.Accordingly, a highly reliable flexible display panel can be achieved.

In this embodiment, a display panel using an EL element as a displayelement will be described as an example.

The display panel can have a structure in which subpixels of threecolors of R (red), G (green), and B (blue) express one color; astructure in which subpixels of four colors of R, G, B, and W (White)express one color; a structure in which subpixels of four colors of R,G, B, and Y (yellow) express one color; or the like. There is nolimitation on color elements, and colors other than R, G, B, W, and Y(e.g., cyan or magenta) may be used. FIGS. 7(A) and 7(B) show top viewsof a display panel 370.

The display panels 370 illustrated in FIGS. 7(A) and 7(B) each includethe visible-light-transmitting region 110, a display portion 381, and adriver circuit portion 382. In FIG. 7(A), an example is shown in whichthe visible-light-transmitting region 110 is adjacent to the displayportion 381 and provided along two sides of the display portion 381. InFIG. 7(B), an example is shown in which the risible-light-transmittingregion 110 is adjacent to the display portion 381 and provided alongthree sides of the display portion 381.

FIG. 7(C) shows a cross-sectional view of the display panel 370employing a color filter method and having a top-emission structure.FIG. 7(C) corresponds to cross-sectional views along dashed-dotted linesA1-A2 and A3-A4 in FIGS. 7(A) and 7(B).

The display panel 370 includes the substrate 201, the bonding layer 203,the first insulating layer 205, the second insulating layer 207, aplurality of transistors, a capacitor 305, a conductive layer 307, aninsulating layer 312, an insulating layer 313, an insulating layer 314,an insulating layer 315, a light-emitting element 304, a conductivelayer 355, a spacer 316, a bonding layer 317, a coloring layer 325, alight-blocking layer 326, the substrate 211, the bonding layer 213, thethird insulating layer 215, and the fourth insulating layer 217. Each ofthe layers included in the visible-light-transmitting region 110transmits visible light.

The driver circuit portion 382 includes a transistor 301. The displayportion 381 includes a transistor 302 and a transistor 303.

Each transistor includes a gate, a gate insulating layer 311, asemiconductor layer, a source, and a drain. The gate and thesemiconductor layer overlap with each other with the gate insulatinglayer 311 provided therebetween. Part of the gate insulating layer 311functions as a dielectric of the capacitor 305. The conductive layerfunctioning as the source or the drain of the transistor 302 also servesas one electrode of the capacitor 305.

FIG. 7(C) shows a bottom gate transistor. The structure of thetransistor may be different between the driver circuit portion 382 andthe display portion 381. The driver circuit portion 382 and the displayportion 381 may each include a plurality of kinds of transistors.

The capacitor 305 includes a pair of electrodes and the dielectrictherebetween. The capacitor 305 includes a conductive layer that isformed using the same material and the same step as the gate of thetransistor and a conductive layer that is formed using the same materialand the same step as the source and the drain of the transistor.

The insulating layer 312, the insulating layer 313, and the insulatinglayer 314 are each provided to cover the transistors and the like. Thenumber of the insulating layers covering the transistors and the like isnot particularly limited. The insulating layer 314 functions as aplanarization layer. A material through which impurities such as waterand hydrogen are less likely to be diffused is preferably used for atleast one of the insulating layer 312, the insulating layer 313, and theinsulating layer 314. Diffusion of impurities from the outside into thetransistor can be effectively suppressed, leading to improvedreliability of the display panel.

The display panel 370 has a structure in which the reflection of lightin the visible-light-transmitting region 110 is suppressed. Thevisible-light-transmitting region 110 includes the substrate 201, thebonding layer 203, the first insulating layer 205, the bonding layer317, the third insulating layer 215, the bonding layer 213, and thesubstrate 211 that are stacked in this order.

The second insulating layer 207, the fourth insulating layer 217, thegate insulating layer 311, the insulating layer 312, the insulatinglayer 313, the insulating layer 314, and the insulating layer 315 areprovided in the display portion 381 and not provided in thevisible-light-transmitting region 110. The end portions of theseinsulating layers are preferably positioned in part of the displayportion 381 that is near the boundary between the display portion 381and the visible-light-transmitting region 110, in addition, the endportions of these insulating layers preferably overlap with thelight-blocking layer 326. Thus, variation in reflectance andtransmittance can be made small on the plane of thevisible-light-transmitting region 110.

The first insulating layer 205 and the substrate 201 are attached toeach other with the bonding layer 203. The third insulating layer 215and the substrate 211 are attached to each other with the bonding layer213. In the manufacturing method of a display panel of one embodiment ofthe present invention, the first insulating layer 205 and the thirdinsulating layer 215 are layers positioned in the separation interfaceswith the respective formation substrates and provided over the entiresurface of the display panel 370. Thus, the display panel 370 can bemanufactured with high yield.

In the display portion 381, the light-emitting element 304 is positionedbetween the second insulating layer 207 and the fourth insulating layer217. Entry of impurities into the light-emitting element 304 from thethickness direction of the display panel 370 is suppressed. Similarly, aplurality of insulating layers covering the transistors are provided inthe display portion 381, and thus entry of impurities into thetransistors is suppressed.

The light-emitting element 304, the transistors, and the like arepreferably provided between a pair of insulating films having a highmoisture-proof property because entry of impurities such as water intothese elements can be suppressed, leading to higher reliability of thedisplay panel.

Examples of an insulating film having a high moisture-proof propertyinclude a film containing nitrogen and silicon such as a silicon nitridefilm or a silicon nitride oxide film and a film containing nitrogen andaluminum such as an aluminum nitride film. Alternatively, a siliconoxide film, a silicon oxynitride film, an aluminum oxide film, or thelike may be used.

For example, the water vapor permeability of the insulating film havinga high moisture-proof property is lower than or equal to 1×10⁻⁵[g/(m²·day)], preferably lower than or equal to 1×10⁻⁶ [g/(m²·day)],further preferably lower than or equal to 1×10⁻⁷ [g/(m²·day)], stillfurther preferably lower than or equal to 1×10⁻⁸ [g/(m²·day)].

In the case where an organic material is used for the insulating layer314, impurities such as moisture might enter the light-emitting element304 and the like from the outside of the display panel through theinsulating layer 314 exposed at an end portion of the display panel.Deterioration of the light-emitting element 304 due to the entry of animpurity leads to deterioration of the display panel. Thus, asillustrated in a portion near a connection portion 306 in FIG. 7(C), anopening that reaches an inorganic film (here, the insulating layer 313)is preferably provided in the insulating layer 314 so that an impuritysuch as moisture entering from the outside of the display panel does noteasily reach the light-emitting element 304.

The light-emitting element 304 includes an electrode 321, an EL layer322, and an electrode 323. The light-emitting element 304 may include anoptical adjustment layer 324. The light-emitting element 304 emits lightto the coloring layer 325 side.

The transistor, the capacitor, the wiring, and the like are provided tooverlap with a light-emitting region of the light-emitting element 304,whereby an aperture ratio of the display portion 381 can be increased.

One of the electrode 321 and the electrode 323 functions as an anode andthe other functions as a cathode. When a voltage higher than thethreshold voltage of the light-emitting element 304 is applied betweenthe electrode 321 and the electrode 323, holes are injected from theanode side and electrons are injected from the cathode side to the ELlayer 322. The injected electrons and holes are recombined in the ELlayer 322 and a light-emitting substance contained in the EL layer 322emits light.

The electrode 321 is electrically connected to a source or a drain ofthe transistor 303. These are connected directly or connected throughanother conductive layer. The electrode 321, which functions as a pixelelectrode, is provided for each light-emitting element 304. Two adjacentelectrodes 321 are electrically insulated from each other by theinsulating layer 315.

The EL layer 322 is a layer containing a light-emitting material. As thelight-emitting element 304, an organic EL element including an organiccompound as a light-emitting material can be favorably used.

The EL layer 322 includes at least one light-emitting layer.

As a light-emitting material, a quantum dot can also be used. A quantumdot is a semiconductor nanocrystal with a size of several nanometers andcontains approximately 1×10³ to 1×10⁶ atoms. Since energy shift ofquantum dots depends on their size, quantum dots made of the samesubstance emit light with different wavelengths depending on their size;thus, emission wavelengths can be easily adjusted by changing the sizeof quantum dots to be used.

A quantum dot has an emission spectrum with a narrow peak, leading toemission with high color purity. In addition, a quantum dot is said tohave a theoretical internal quantum efficiency of approximately 100%,and a quantum dot can be used as a light-emitting material to obtain alight-emitting element having high light emission efficiency.Furthermore, since a quantum dot that is an inorganic compound has highinherent stability, a light-emitting element that is preferable also interms of lifetime can be obtained.

Examples of a material of a quantum dot include a Group 14 element inthe periodic table, a Group 15 element in the periodic table, a Group 16element in the periodic table, a compound of a plurality of Group 14elements in the periodic table, a compound of an element belonging toany of a Group 4 to a Group 14 in the periodic table and a Group 16element in the periodic table, a compound of a Group 2 element in theperiodic table and a Group 16 element in the periodic table, a compoundof a Group 13 element in the periodic table and a Group 15 element inthe periodic table, a compound of a Group 13 element in the periodictable and a Group 17 element in the periodic table, a compound of aGroup 14 element in the periodic table and a Group 15 element in theperiodic table, a compound of a Group 11 element in the periodic tableand a Group 17 element in the periodic table, iron oxides, titaniumoxides, spinel chalcogenides, and semiconductor clusters.

Examples of a material included in a quantum dot include cadmiumselenide, cadmium sulfide, cadmium telluride, zinc sulfide, indiumphosphide, lead selenide, lead sulfide, a compound of selenium, zinc,and cadmium, and a compound of cadmium, selenium, and sulfur. What iscalled an alloyed quantum dot, whose composition is represented by agiven ratio, may be used. For example, an alloyed quantum dot ofcadmium, selenium, and sulfur is a means effective in obtaining bluelight because the emission wavelength can be changed by changing thecontent ratio of elements.

As the structure of the quantum dot, any of a core type, a core-shelltype, a core-multishell type, and the like may be used. It is preferableto use a core-shell or core-multishell quantum dot because the quantumefficiency of light emission can be significantly improved. Examples ofthe material of a shell include zinc sulfide and zinc oxide.

Quantum dots have a high proportion of surface atoms and thus have highreactivity and easily cohere together. For this reason, it is preferablethat a protective agent be attached to, or a protective group beprovided at the surfaces of quantum dots. In this manner, cohesion ofquantum dots can be prevented and solubility in a solvent can beincreased. It can also reduce reactivity and improve electricalstability.

The range of size (diameter) of quantum dots, which is greater than orequal to 0.5 nm and less than or equal to 20 nm, preferably greater thanor equal to 1 nm and less than or equal to 10 nm, is usually used. Notethat the emission spectra are narrowed as the size distribution of thequantum dots gets smaller, and thus light can be obtained with highcolor purity. The shape of the quantum dots is not particularly limitedand may be a spherical shape, a rod shape, a circular shape, or anothershape.

As for quantum dots, even when a light-emitting layer is composed ofonly quantum dots and made without a host material, light emissionefficiency can be ensured; thus, a light-emitting element that isfavorable in terms of a lifetime can be obtained. In the case where thelight-emitting layer is composed of only quantum dots, the quantum dotspreferably have core-shell structures (including core-multishellstructures).

The electrode 323, which functions as a common electrode, is providedfor a plurality of light-emitting elements 304. A fixed potential issupplied to the electrode 323.

The light-emitting element 304 overlaps with the coloring layer 325 withthe bonding layer 317 provided therebetween. The spacer 316 overlapswith the light-blocking layer 326 with the bonding layer 317 providedtherebetween. Although FIG. 7(C) illustrates the case where a space isprovided between the light-emitting element 304 and the light-blockinglayer 326, these may be in contact with each other. Although a structurein which the spacer 316 is provided on the substrate 201 side isillustrated in FIG. 7(C), the spacer 316 may be provided on thesubstrate 211 side (e.g., on a side closer to the substrate 201 than thelight-blocking layer 326).

Owing to the combination of a color filter (the coloring layer 325) anda microcavity structure (the optical adjustment layer 324), light withhigh color purity can be extracted from the display panel. The thicknessof the optical adjustment layer 324 is varied depending on the color ofthe pixel.

The coloring layer is a colored layer that transmits light in a specificwavelength range. For example, a color filter or the like fortransmitting light in a red, green, blue, or yellow wavelength range canbe used. Examples of materials that can be used for the coloring layerinclude a metal material, a resin material, and a resin materialcontaining a pigment or dye.

Note that one embodiment of the present invention is not limited to acolor filter method, and a separate coloring method, a color conversionmethod, a quantum dot method, or the like may be employed.

The light-blocking layer is provided between the adjacent coloringlayers. The light-blocking layer blocks light from an adjacentlight-emitting element to suppress color mixture between adjacentlight-emitting elements. Here, an end portion of the coloring layer isprovided so as to overlap with the light-blocking layer, whereby lightleakage can be reduced. As the light-blocking layer, a material thatblocks light from the light-emitting element can be used; for example, ablack matrix can be formed using a metal material or a resin materialcontaining a pigment or dye. Note that the light-blocking layer ispreferably provided in a region other than a pixel portion, such as adriver circuit, because unintended light leakage due to guided light orthe like can be suppressed.

The connection portion 306 includes the conductive layer 307 and theconductive layer 355. The conductive layer 307 and the conductive layer355 are electrically connected to each other. The conductive layer 307can be formed using the same material and the same step as those of thesource and the drain of the transistor. The conductive layer 355 iselectrically connected to an external input terminal that transmits asignal or a potential from the outside to the driver circuit portion382. Here, an example in which an FPC 373 is provided as an externalinput terminal is shown. The FPC 373 and the conductive layer 355 areelectrically connected to each other through a connector 319.

As the connector 319, various anisotropic conductive films (ACF),anisotropic conductive pastes (ACP), and the like can be used.

The transistors 301, 302, and 303 illustrated in FIG. 9(A) each includetwo gates, the gate insulating layer 311, a semiconductor layer, asource, and a drain. FIG. 9(A) illustrates an example in which eachtransistor has a structure in which the semiconductor layer issandwiched between the two gates. Such a transistor can have higherfield-effect mobility and thus have higher on-state current than othertransistors. Consequently, a circuit capable of high-speed operation canbe manufactured. Furthermore, the area occupied by the circuit can bereduced. With the use of the transistor having a high on-state current,signal delay in each wiring can be reduced and display luminancevariation can be reduced even if the number of wirings is increased whenthe size or resolution of a display panel is increased. In FIG. 9(A), anexample in which one of the gates is formed between the insulating layer313 and the insulating layer 314 is shown.

As illustrated in FIG. 9(A), a display panel preferably includes anovercoat 329. The overcoat 329 can prevent impurities and the likecontained in the coloring layer 325 from being diffused into thelight-emitting element 304. The overcoat 329 is formed using a materialthat transmits light from the light-emitting element 304. For example,it is possible to use an inorganic insulating film such as a siliconnitride film or a silicon oxide film or an organic insulating film suchas an acrylic film or a polyimide film, and a stacked-layer structure ofan organic insulating film and an inorganic insulating film may beemployed. In FIG. 9(A), an example in which the overcoat 329 ispositioned over the entire surface of the display panel is shown. Theovercoat 329 is not necessarily provided in thevisible-light-transmitting region 110.

In the case where a material of the bonding layer 317 is coated on thecoloring layer 325 and the light-blocking layer 326, a material whichhas high wettability with respect to the material of the bonding layer317 is preferably used as the material of the overcoat 329. For example,an oxide conductive film such as an indium tin oxide (ITO) film or ametal film such as an Ag film which is thin enough to have alight-transmitting property is preferably used as the overcoat 329.

The material of the bonding layer 317 can be uniformly coated on theovercoat 329 by using a material which has high wettability with respectto the material of the bonding layer 317. Accordingly, entry of bubblesin attaching the pair of substrates to each other can be suppressed, andthus a display defect can be suppressed.

A substrate having flexibility is preferably used as the substrate 201and the substrate 211. For example, a material such as glass, quartz, aresin, a metal, an alloy, or a semiconductor thin enough to haveflexibility can be used. A material which transmits light from thelight-emitting element is used for the substrate on the side from whichthe light is extracted. For example, the thickness of the substrate ispreferably greater than or equal to 1 μm and less than or equal to 200μm, further preferably greater than or equal to 1 μm and less than orequal to 100 μm, still further preferably greater than or equal to 10 μmand less than or equal to 50 μm, and particularly preferably greaterthan or equal to 10 μm and less than or equal to 25 μm. The thicknessand hardness of the substrate having flexibility are set in the rangewhere mechanical strength and flexibility can be balanced against eachother. The substrate having flexibility may have a single-layerstructure or a stacked-layer structure.

A resin, which has a specific gravity smaller than that of glass, ispreferably used for the substrate having flexibility, because thedisplay panel can be lightweight as compared with the case where glassis used.

A material with high toughness is preferably used for the substrate. Inthat case, a display panel with high impact resistance that is lesslikely to be broken can be provided. For example, when a resin substrateor a thin metal or alloy substrate is used, the display panel that islightweight and less likely to be broken as compared with the case wherea glass substrate is used can be achieved.

A metal material and an alloy material are preferable because they havehigh thermal conductivity and can easily conduct heat to the wholesubstrate, and a local temperature rise in the display panel can besuppressed. The thickness of a substrate using a metal material or analloy material is preferably greater than or equal to 10 μm and lessthan or equal to 200 μm, further preferably greater than or equal to 20μm and less than or equal to 50 μm.

Although a material that forms the metal substrate or the alloysubstrate is not particularly limited, it is favorable to use, forexample, aluminum, copper, nickel, or a metal alloy such as an aluminumalloy or stainless steel. Examples of a material that forms asemiconductor substrate include silicon.

Furthermore, when a material with high thermal emissivity is used forthe substrate, increase of the surface temperature of the display panelcan be suppressed, and breakage or a decrease in reliability of thedisplay panel can be suppressed. For example, the substrate may have astacked-layer structure of a metal substrate and a layer with highthermal emissivity (e.g., a metal oxide or a ceramic material can beused).

Examples of materials having flexibility and a light-transmittingproperty include polyester resins such as PET and PEN, apolyacrylonitrile resin, an acrylic resin, a polyimide resin, apolymethyl methacrylate resin, a PC resin, a PES resin, polyamide resins(such as nylon and aramid), a polysiloxane resin, a cycloolefin resin, apolystyrene resin, a polyamide-imide resin, a polyurethane resin, apolyvinyl chloride resin, a polyvinylidene chloride resin, apolypropylene resin, a PTFE resin, and an ABS resin. In particular, amaterial whose linear thermal expansion coefficient is reduced ispreferably used, and for example, a polyamide imide resin, a polyimideresin, a polyamide resin, PET, or the like can be favorably used. Asubstrate in which a fibrous body is impregnated with a resin, asubstrate whose linear thermal expansion coefficient is reduced bymixing an inorganic filler with a resin, or the like can also be used.

The substrate having flexibility may be formed by stacking a layer usingthe above-described materials with at least one of a hard coat layer bywhich a surface of the device is protected from damage or the like(e.g., a silicon nitride layer), a layer of a material which candisperse pressure (e.g., an aramid resin layer), and the like. Asubstrate that can be used as a protective substrate 132 may be used.

When a glass layer is included in the substrate having flexibility, abarrier property against water and oxygen can be improved and thus ahighly reliable display panel can be provided.

For the bonding layer, a variety of curable adhesives such as aphotocurable adhesive such as an ultraviolet curable adhesive, areactive curable adhesive, a thermosetting adhesive, and an anaerobicadhesive can be used. Alternatively, an adhesive sheet or the like maybe used.

Furthermore, the bonding layer may include a drying agent. For example,it is possible to use a substance that adsorbs moisture by chemicaladsorption, such as oxide of an alkaline earth metal (calcium oxide,barium oxide, or the like). Alternatively, it is possible to use asubstance that adsorbs moisture by physical adsorption, such as zeoliteor silica gel. The drying agent is preferably included because entry ofimpurities such as moisture into the functional element can besuppressed, thereby improving the reliability of the display panel.

When a filler with a high refractive index or a light scattering memberis contained in the bonding layer, the efficiency of light extractionfrom the light-emitting element can be improved. For example, titaniumoxide, barium oxide, zeolite, or zirconium can be used.

As the light-emitting element, a self-luminous element can be used, andan element whose luminance is controlled by current or voltage isincluded in its category. For example, a light-emitting diode (LED), anorganic EL element, an inorganic EL element, or the like can be used.Note that a variety of display elements can be used for the displaypanel of one embodiment of the present invention. For example, a liquidcrystal element, an electrophoretic element, a display element usingMEMS, or the like may be used.

The light-emitting element may be of a top-emission, bottom-emission, ordual-emission type. A visible-light-transmitting conductive film is usedfor the electrode through which light is extracted. Avisible-light-reflecting conductive film is preferably used for theelectrode through which light is not extracted.

The visible-light-transmitting conductive film can be formed using, forexample, indium oxide, ITO, indium zinc oxide, zinc oxide (ZnO), or ZnOto which gallium is added. Alternatively, a metal material such as gold,silver, platinum, magnesium, nickel, tungsten, chromium, molybdenum,iron, cobalt, copper, palladium, or titanium; an alloy containing thesemetal materials; a nitride of these metal materials (e.g., titaniumnitride); or the like can be used when formed thin so as to have alight-transmitting property. Alternatively, a stacked film of the abovematerials can be used as the conductive film. For example, a stackedfilm of an alloy of silver and magnesium, and ITO is preferably used,because conductivity can be increased. Alternatively, graphene or thelike may be used.

For the visible-light-reflecting conductive film, for example, a metalmaterial such as aluminum, gold, platinum, silver, nickel, tungsten,chromium, molybdenum, iron, cobalt, copper, or palladium or an alloycontaining any of these metal materials can be used. Furthermore,lanthanum, neodymium, germanium, or the like may be added to the metalmaterial or the alloy. Furthermore, an alloy containing aluminum (analuminum alloy) such as an alloy of aluminum and titanium, an alloy ofaluminum and nickel, an alloy of aluminum and neodymium, or an alloy ofaluminum, nickel, and lanthanum (Al—Ni—La) or an alloy containing silversuch as an alloy of silver and copper, an alloy of silver, palladium,and copper (Ag—Pd—Cu, also referred to as APC), or an alloy of silverand magnesium may be used. An alloy containing silver and copper ispreferable because of its high heat resistance. Furthermore, when ametal film or a metal oxide film that is in contact with an aluminumalloy film is stacked, oxidation of the aluminum alloy film can besuppressed. Examples of materials of the metal film or the metal oxidefilm include titanium and titanium oxide. Alternatively, the abovevisible-light-transmitting conductive film and a film formed of a metalmaterial may be stacked. For example, a stacked film of silver and ITOor a stacked film of an alloy of silver and magnesium and ITO can beused.

Each of the electrodes can be formed by an evaporation method or asputtering method. Alternatively, a discharging method such as an inkjetmethod, a printing method such as a screen printing method, or a platingmethod may be used.

The EL layer 322 includes at least a light-emitting layer. The EL layer322 may include a plurality of light-emitting layers. In addition to thelight-emitting layer, the EL layer 322 may further include a layercontaining a substance with a high hole-injection property, a layercontaining a substance with a high hole-transport property, a layercontaining a hole-blocking material, a layer containing a substance witha high electron-transport property, a layer containing a substance witha high electron-injection property, a layer containing a substance witha bipolar property (a substance with a high electron- and hole-transportproperty), or the like.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer 322, and an inorganic compound may also be contained.Each of the layers that form the EL layer 322 can be formed by a methodsuch as an evaporation method (including a vacuum evaporation method), atransfer method, a printing method, an inkjet method, or a coatingmethod.

The light-emitting element 304 may contain two or more kinds oflight-emitting substances. Thus, for example, a light-emitting elementthat emits white light can be achieved. A white emission can be obtainedby selecting light-emitting substances so that two or more kinds oflight-emitting substances emit light of complementary colors, forexample. A light-emitting substance that emits light of R (red), G(green), B (blue), Y (yellow), O (orange), or the like or alight-emitting substance that emits light containing spectral componentsof two or more colors of R, G, and B can be used, for example.

Moreover, the light-emitting element 304 may be a single elementincluding one EL layer or a tandem element including a plurality of ELlayers stacked with a charge generation layer provided therebetween.

<Structure Example Of Light-Emitting Panel>

Cross-sectional views of display panels 370A and 370B employing aseparate coloring method and having a top-emission structure areillustrated in FIG. 9(A) and FIG. 9(B). A color filter is included inFIG. 9(A). If not necessary, a structure without a color filter asillustrated in FIG. 9(B) may be employed. In these cases, light-emittinglayers of the light-emitting elements for respective colors arepreferably separated. A display device of one embodiment of the presentinvention is composed of a plurality of display panels, and each displaypanel can have a relatively small size. Thus, the alignment accuracy ofa metal mask can be raised, leading to higher yield in separatecoloring. Accordingly, there is an advantage in that light-emittingelements using a separate coloring method are employed.

The structure of the transistors included in the display panel is notparticularly limited. For example, a planar transistor may be used, astaggered transistor may be used, or an inverted staggered transistormay be used. Either a top-gate transistor or a bottom-gate transistormay be used. Alternatively, gate electrodes may be provided above andbelow a channel.

There is no particular limitation on the crystallinity of thesemiconductor material used for the transistor, and either an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. A semiconductor having crystallinity ispreferably used because deterioration in the transistor characteristicscan be suppressed.

A semiconductor material used for the transistor is not particularlylimited, and for example, a Group 14 element, a compound semiconductor,or an oxide semiconductor can be used for a semiconductor layer.Typically, a semiconductor containing silicon, a semiconductorcontaining gallium arsenide, an oxide semiconductor containing indium,or the like can be used.

It is particularly preferable to use an oxide semiconductor as asemiconductor in which a channel of the transistor is formed. Inparticular, an oxide semiconductor having a wider band gap than siliconis preferably used. A semiconductor material having a wider band gap anda lower carrier density than silicon is preferably used because thecurrent in an off state of the transistor can be reduced.

For example, at least indium (In) or zinc (Zn) is preferably containedas the oxide semiconductor. Further preferably, an oxide represented byan In-M-Zn oxide (M is a metal such as Al, Ti, Ga, Ge, Y, Zr, Sn, La,Ce, Hf, or Nd) is contained.

A CAAC-OS (C Axis Aligned Crystalline Oxide Semiconductor) is preferablyused as a semiconductor material used for the transistors. Unlike anamorphous state, the CAAC-OS has few defect levels, so that thereliability of the transistor can be improved. Moreover, since theCAAC-OS has a feature in that no grain boundary is observed, a stableand uniform film can be formed over a large area, and stress that iscaused by curving a display panel having flexibility does not easilymake a crack in a CAAC-OS film.

The CAAC-OS is a crystalline oxide semiconductor in which c-axes ofcrystals are oriented in a direction substantially perpendicular to thefilm surface. It has been found that oxide semiconductors have a varietyof crystal structures other than a single-crystal structure, such as ananocrystal (nc) structure, which is an aggregate of nanoscalemicrocrystals. A CAAC-OS has lower crystallinity than a single crystaland higher crystallinity than nc.

The CAAC-OS has c-axis alignment, its pellets (nanocrystals) areconnected in an a-b plane direction, and the crystal structure hasdistortion. Thus, the CAAC-OS can also be referred to as an oxidesemiconductor including a CAA crystal (c-axis-aligned a-b-plane-anchoredcrystal).

An organic insulating material or an inorganic insulating material canbe used for the insulating layers included in the display panel.Examples of resins include an acrylic resin, an epoxy resin, a polyimideresin, a polyamide resin, a polyimide-amide resin, a siloxane resin, abenzocyclobutene-based resin, and a phenol resin. Examples of inorganicinsulating films include a silicon oxide film, a silicon oxynitridefilm, a silicon nitride oxide film, a silicon nitride film, an aluminumoxide film, a hafnium oxide film, an yttrium oxide film, a zirconiumoxide film, a gallium oxide film, a tantalum oxide film, a magnesiumoxide film, a lanthanum oxide film, a cerium oxide film, and a neodymiumoxide film.

The conductive layers included in the display panel can each have asingle-layer structure or a stacked-layer structure including any ofmetals such as aluminum, titanium, chromium, nickel, copper, yttrium,zirconium, molybdenum, silver, tantalum, and tungsten or an alloycontaining any of these metals as its main component. Alternatively, aconductive material having a light-transmitting property such as indiumoxide, ITO, indium oxide containing tungsten, indium zinc oxidecontaining tungsten, indium oxide containing titanium, ITO containingtitanium, indium zinc oxide, ZnO, ZnO to which gallium is added, orindium tin oxide containing silicon may be used. Alternatively, asemiconductor such as polycrystalline silicon or an oxide semiconductorwhose resistance is lowered, for example, by containing an impurityelement, or silicide such as nickel silicide may be used. A filmcontaining graphene may be used as well. The film containing graphenecan be formed, for example, by reducing a film containing grapheneoxide. A semiconductor such as an oxide semiconductor containing animpurity element may be used. Alternatively, the conductive layers maybe formed using a conductive paste of silver, carbon, copper, or thelike or a conductive polymer such as a polythiophene. A conductive pasteis preferable because it is inexpensive. A conductive polymer ispreferable because it is easily coated.

An example of a cross-sectional view of a display device including twodisplay panels 370 illustrated in FIG. 7(C) that overlap with each otheris illustrated in FIG. 8.

In FIG. 8, the following are illustrated: the display region 101 a(corresponding to the display portion 381 in FIG. 7(C)) and a region 120a that blocks visible light (corresponding to the driver circuit portion382 and the like in FIG. 7(C)) of a lower display panel, and the displayregion 101 b (corresponding to the display portion 381 in FIG. 7(C)) andthe visible-light-transmitting region 110 b (corresponding to thevisible-light-transmitting region 110 in FIG. 7(C)) of an upper displaypanel.

In the display device illustrated in FIG. 8, the display panelpositioned on the display surface side (upper side) includes thevisible-light-transmitting region 110 b adjacent to the display region101 b. The display region 101 a of the lower display panel overlaps withthe visible-light-transmitting region 110 b of the upper display panel.Thus, a non-display region between the display regions of the twodisplay panels overlapping with each other can be reduced or evenremoved. Accordingly, a large display device in which a seam betweendisplay panels is less likely to be noticed by a user can be achieved.

The display device illustrated in FIG. 8 includes a light-transmittinglayer 103 having a refractive index higher than that of air andtransmitting visible light between the display region 101 a and thevisible-light-transmitting region 110 b. Accordingly, entry of airbetween the display region 101 a and the visible-light-transmittingregion 110 b can be suppressed, so that the interface reflection due toa difference in refractive index can be reduced. In addition, displayunevenness or luminance unevenness in the display device can besuppressed.

The light-transmitting layer 103 may overlap with the entire surface ofthe substrate 211 of the lower display panel or the substrate 201 of theupper display panel, or may overlap with only the display region 101 aand the visible-light-transmitting region 110 b. In addition, thelight-transmitting layer 103 may overlap with the region 120 a thatblocks visible light.

For example, an adsorption film having adsorption layers on bothsurfaces of a base material can be used as the light-transmitting layer103.

The visible-light-transmitting region 110 b has a structure in which thereflection of light is suppressed. Thus, a portion in which the twodisplay panels overlap with each other (an overlapping portion) is lesslikely to be seen by a user of the display device. Moreover, in thedisplay in the display region 101 a, a difference in luminance between aportion seen through the visible-light-transmitting region 110 b and aportion seen not through the region can be made small.

This embodiment can be freely combined with the other embodiments.

Example 1

In this example, results of fabricating the display device of oneembodiment of the present invention will be described. A display devicefabricated in this example is a kawara-type multi display.

<Display Panel>

First, the display panel used in the display device in this example willbe described in detail.

A schematic view of the display panel in this example is illustrated inFIG. 10(A). The display panel illustrated in FIG. 10(A) is an activematrix organic EL display that has a light-emitting portion 250 with adiagonal size of 13.5 inches, 1280×720 effective pixels, a resolution of108 ppi, and an aperture ratio of 41.3%. The display panel includes abuilt-in demultiplexer (DeMUX) 253, which functions as a source driver.In addition, the display panel also includes a built-in scan driver 255.TWO sides of the light-emitting portion 250 are in contact with avisible-light-transmitting region 251. A lead wiring 257 is providedalong the other two sides.

A channel-etched transistor including a CAAC-OS was used as thetransistor. Note that an In—Ga—Zn-based oxide was used as the oxidesemiconductor.

As the light-emitting elements, three types of organic EL elements ofRGB were used. A structure in which light from the light-emittingelement is extracted to the outside of the display panel through thecolor filter is employed. The light-emitting element has a top-emissionstructure.

FIG. 10(B) illustrates a schematic view of a display device in whichthree display panels overlap with one another to have a T-shape. FIG.10(C) illustrates a cross-sectional schematic view taken along a dasheddotted line X-Y of the display device of FIG. 10(B).

The display device in this example is formed by overlapping a pluralityof display panels so that a non-display region between display regionsbecomes small. Specifically, the light-transmitting layer 103 isprovided between the visible-light-transmitting region 251 of an upperdisplay panel and the light-emitting portion 250 of a lower displaypanel.

From an end portion of the light-emitting portion 250 to an end portionof the display panel along two sides of the display panel, a componentthat blocks visible light such as a lead wiring or a driver is notprovided and the region along two sides serves as thevisible-light-transmitting region 251. The width of thevisible-light-transmitting region 251 of the display panel wasapproximately 5 mm. The thickness T of the visible-light-transmittingregion 251 (also referred to as a thickness of one display panel) isapproximately 110 μm, which is very small. Therefore, although thedisplay device in this example has a portion in which at most threedisplay panels overlap with one another, a step generated on the displaysurface side is extremely small; thus, a seam is less likely to benoticed.

The three display panels have flexibility. For example, as illustratedin FIG. 10(C), a region near an FPC 373 a of the lower display panel canbe curved so that part of the lower display panel and part of the FPC373 a can be placed under the light-emitting portion 250 of the upperdisplay panel adjacent to the FPC 373 a. As a result, the FPC 373 a canbe placed without physical interference with the rear surface of theupper display panel. In this way, another display panel can be providedon four sides of the display panel, whereby a large-sized display deviceis easily achieved.

In this example, an adsorption film including adsorption layers on bothsurfaces of a base material was used as the light-transmitting layer103. With the use of the adsorption film, two display panels included inthe display device can be detachably attached to each other. Anadsorption layer on one side of the light-transmitting layer 103 isadsorbed onto a substrate 211 a, and an adsorption layer on the otherside of the light-transmitting layer 103 is adsorbed onto a substrate201 b.

In FIG. 10(B), the light-transmitting layer 103 includes not only aportion overlapping with the visible-light-transmitting region 251 butalso a portion overlapping with the light-emitting portion 250. In FIG.10(C), the light-transmitting layer 103 overlaps with the entirevisible-light-transmitting region 251 from an end portion of thesubstrate 201 b, and also overlaps with part of a region 155 b includinga display element. Note that the light-transmitting layer 103 is notprovided on a curved portion of the display panel near a portion towhich the FPC 373 a is connected in FIG. 10(C). However, thelight-transmitting layer 103 may be provided depending on the thicknessof the light-transmitting layer 103 or the thickness of a flexiblesubstrate.

Each of the display panels was formed by attaching a substrate and anelement layer with a bonding layer. For example, as illustrated in FIG.10(C), a substrate 201 a, the substrate 211 a, the substrate 201 b, anda substrate 211 b are attached to an element layer 153 a, the elementlayer 153 a, an element layer 153 b, and the element layer 153 b,respectively, with a bonding layer 157. The element layer 153 a has aregion 155 a including a display element and a region 156 a including awiring electrically connected to the display element. Similarly, theelement layer 153 b has the region 155 b including a display element anda region 156 b including a wiring electrically connected to the displayelement.

FIG. 11 illustrates a cross-sectional view of a display device includingan overlapping portion of two display panels.

The structures of the light-emitting portion 250 and thevisible-light-transmitting region 251 of the display panels used in thisexample will be described with reference to FIG. 11. The structures of alight-emitting portion 250 a and a light-emitting portion 250 b aresimilar to each other, and thus they are collectively described as thelight-emitting portion 250. The light-emitting portion 250 and thevisible-light-transmitting region 251 include the first insulating layer205, the second insulating layer 207, the gate insulating layer 311, theinsulating layer 312, the third insulating layer 215, and the fourthinsulating layer 217. The insulating layer 313, the insulating layer314, and the insulating layer 315 are provided in the light-emittingportion 250 and not provided in the visible-light-transmitting region251. The display panel in this example has a structure similar to thatof the display panel 370A in FIG. 9(A) described in Embodiment 4 otherthan the structure of the visible-light-transmitting region 251.

FIG. 12(A) is a photograph of the actually fabricated panel. FIG. 12(A)illustrates a state where an end portion of the display panel on theright side is pushed out by a position adjustment function from the rearside of the display panel to be curved and the video of the rear portion(the side mirror video) is displayed on the circular region. The videodisplayed in FIG. 12(A) is image video, and video shot by a camera (theside mirror video) is displayed on the circular region in the case wherethe panel is actually mounted on a car. Naturally, the curved portioncan be undone by the position adjustment function. FIG. 12(B) is aphotograph of the undone panel. Note that the video displayed in thedisplay device of FIG. 12(B) displays car navigation video.

FIG. 13 illustrates an example of a position adjustment jig 21 thatpushes out part of the display panel on the right side. FIG. 13illustrates a state where the periphery of the display panel 100 ispushed out to be in a position indicated by a dotted line. One end ofthe display panel is moved in such a manner that the position adjustmentjig 21 is moved by rotating a rotation axis 23 indicated by a chain lineby a motor 22. A region with a radius of about 14.5 cm with one end ofthe display panel as its center is pushed up, and the one end of thedisplay panel that is pushed up is lifted up to about 5 cm from the flatplane of the display panel.

FIG. 14(A) shows a photograph taken from the side of the display panelin a partly pushed state. FIG. 14(B) shows a photograph taken from theside in a state where the position adjustment jig 21 is undone. Asillustrated in FIG. 14(B), the side mirror video is displayed on acircular region. Note that the display images are all image data.

REFERENCE NUMERALS

-   10 display device-   11 display device-   12 display device-   13 display device-   21 position adjustment jig-   22 motor-   23 rotation axis-   100 display panel-   101 display region-   103 light-transmitting layer-   110 region-   112 FPC-   120 region-   132 protective substrate-   153 a element layer-   153 b element layer-   155 a region-   155 b region-   156 a region-   156 b region-   157 bonding layer-   161 portion-   162 portion-   163 portion-   165 portion-   166 optical member-   167 position adjustment unit-   168 portion-   201 substrate-   201 a substrate-   201 b substrate-   203 bonding layer-   205 insulating layer-   207 insulating layer-   209 element layer-   211 substrate-   211 a substrate-   211 b substrate-   213 bonding layer-   215 insulating layer-   217 insulating layer-   221 bonding layer-   223 connection terminal-   231 formation substrate-   233 separation layer-   250 light-emitting portion-   250 a light-emitting portion-   250 b light-emitting portion-   251 region-   255 scan driver-   257 wiring-   301 transistor-   302 transistor-   303 transistor-   304 light-emitting element-   305 capacitor-   306 connection portion-   307 conductive layer-   311 gate insulating layer-   312 insulating layer-   313 insulating layer-   314 insulating layer-   315 insulating layer-   316 spacer-   317 bonding layer-   319 connector-   321 electrode-   322 EL layer-   323 electrode-   324 optical adjustment layer-   325 coloring layer-   326 light-blocking layer-   329 overcoat-   355 conductive layer-   370 display panel-   370A display panel-   370B display panel-   373 FPC-   373 a FPC-   381 display portion-   382 driver circuit portion-   5001 dashboard-   5002 display device-   5002 a display region-   5002 b display region-   5002 c display region-   5002 d display region-   5002 e left-edge portion-   5003 handle-   5004 windshield-   5005 camera-   5006 ventilation duct

The invention claimed is:
 1. A display device comprising: a firstdisplay panel, a second display panel, and a third display panel, and aposition adjustment jig configured to curve an end portion of at leastone of the first to third display panels, wherein the first displaypanel comprises a first region and a second region, wherein the seconddisplay panel comprises a third region and a fourth region, wherein thethird display panel comprises a fifth region and a sixth region, whereinthe first region, the third region, and the fifth region are eachconfigured to transmit visible light, wherein the second region, thefourth region, and the sixth region are each configured to performdisplay, wherein a display region of the display device has a T-shape,and wherein in a first portion, the sixth region of the third displaypanel, the third region of the second display panel, and the firstregion of the first display panel overlap with one another.
 2. Thedisplay device according to claim 1, wherein one of the first displaypanel and the second display panel is flexible and comprises anadjustment function of curving an end portion.
 3. The display deviceaccording to claim 1, further comprising: a first terminal portion on along side of the first display panel.
 4. The display device according toclaim 1, wherein a display area of the first display panel and a displayarea of the second display panel are the same.
 5. The display deviceaccording to claim 1, wherein the first display panel comprises anorganic light-emitting element.
 6. A display device comprising: adisplay panel comprising an organic light-emitting element over aflexible film; an optical film over the display panel; and a positionadjustment jig below a portion in which the optical film and theflexible film overlap with each other, the position adjustment jigconfigured to curve an end portion of the display panel, wherein boththe optical film and the flexible film are curved by a driving mechanismof the position adjustment jig, wherein a display region of the displaypanel has a T-shape, and wherein the display region comprises at least afirst display portion of a first display panel, a second display portionof a second display panel, and a third display portion of a thirddisplay panel.